Quantiferon-TB Gold Plus (QFT-Plus)

Brief Description

QuantiFERON-TB Gold Plus (QFT-Plus) test is the fourth generation in QuantiFERON-TB testing technology assessing cell-mediated response through a quantitative measurement of IFN-γ in a whole blood sample. QFT-Plus is a test that measures the cell-mediated immune (CMI) responses to peptide antigens that simulate mycobacterial proteins. These proteins, ESAT-6 and CFP-10 are absent from all BCG strains and from most non-tuberculosis mycobacteria except for M. kansasii, M. szulgai and M. marinum (1). Individuals infected with M. tuberculosis complex organisms usually have lymphocytes in their blood that recognize these and other mycobacterial antigens. This recognition process involves the generation and secretion of the cytokine, IFN-γ. The detection and subsequent quantification of IFN-γ forms the basis of this test.

Laboratory Unit



Chemiluminescence Immunoassay (CLIA)

Specimen Collection

Whole blood:

Collect 1 ml of blood by venipuncture directly into each of the QFT-Plus Blood Collection Tubes. Immediately after collection, invert tubes 10 times and incubate the QFT-Plus Blood Collection Tubes UPRIGHT at 37°C ± 1°C for 16 to 24 hours. The incubator does not require CO2 or humidification. The incubation time should be noted on the sample.


After incubation of the blood collection tubes at 37°C ± 1°C, tubes may be held at 4-27°C during transit for up to three days prior to centrifugation.  If centrifuged prior to shipping, centrifuge for 15 minutes at 2000 to 3000 RCF (g).  Samples can be maintained at refrigerated temperature (2-8°C) during transit for no more than 28 days after centrifuging.

Acceptable Specimen Type(s)

Whole Blood/Plasma

Test Request

Possible Results

  • Positive
  • Negative
  • Indeterminate
  • Unsatisfactory

Reference Range


Unacceptable Conditions

  • Missing testing requisition
  • Missing minimum of 2 patient identifiers
  • Improper labeling
  • Improper storage/transport of specimen
  • No specimen received (empty collection tube)
  • Wrong specimen type
  • Low volume
  • Specimens damaged, broken, or leaking upon arrival
  • Specimen grossly hemolyzed, lipemic, turbid, or contaminated 
  • Received refrigerated specimen over 28 days old

Interfering Substances

  • Heterophilic antibodies
  • Over vigorous shaking may cause gel disruption and could lead to aberrant results.
  • Hemolysis, lipemia, turbidity, microbial contamination, particulate matter or erythrocyte debris

Result Reported

2-5 business days


No charge

LOINC/Order Codes

45323-3 (Order code: 34900)